Study Notes: Quantitative GC

The technique of GC can be used for qualitative analysis (identifying
the presence or absence of certain analytes in a sample) and quantitative
analysis (determining the concentration of analytes).

In quantitative GC, the area under a peak or peak height is indicative
of the concentration of the component represented by the peak. At SimuLab,
the chart recorder on the virtual GC has an integrator that electronically
determines and displays peak areas (which are reported as a unitless number).
The bigger the peak area, the greater the concentration.

Let us consider the quantitation of ethyl acetate in beer. This compound
is important as it is very flavour-active and contributes to the overall
character of a beer-type.

The Beer Standard chromatogram prepared for the detection of can lacquer
contamination also shows a peak for ethyl acetate – the analytical
and instrumental conditions selected for measurement of the contaminants
are also suitable for ethyl acetate. SimuLab also uses this procedure
is analysis of ethyl acetate in beer.

SimuLab quantitates ethyl acetate in beer by preparing a standard curve
of concentration versus peak area for a range of ethyl acetate standard
solutions. The standards are analysed under the same GC conditions as
used for the samples – their concentration range spans that anticipated
for the samples.

The standard curve shows that an ethyl acetate peak area of 40 000 equates
to a concentration of 20.0 mg/L in the beer sample.